One of the reasons could be that the password for the SYSMAN user is expired. However, changing the password alone will not solve this issue. Several additional steps are required in order to make Oracle Enterprise Manager connect:

Before you start: Verify that ORACLE_HOME, ORACLE_SID environment variables are set. – If not, set them using as  environment variables or open a command line and type SET ORACLE_SID=

1. Stop the dbconsole: emctl stop dbconsole (dos and Unix) or  using the windows services stop the OrcleDBConsole.

2. Connect to the database as a user with DBA privilege with SQL*Plus

and run the following command:

alter user sysman identified by ;

3. Verify that the new password works

SQL> connect sysman/

4. Go to ORACLE_HOME//sysman/config and save a backup of the emoms.properties file.

a) Open the file emoms.properties and search for:

oracle.sysman.eml.mntr.emdRepPwd=

Replace the encrypted value with the new password value

b) Search for oracle.sysman.eml.mntr.emdRepPwdEncrypted=TRUE

and change TRUE to FALSE

c) Save and close emoms.properties

5. Restart the dbconsole:

emctl start dbconsole (dos and Unix) or  using the windows services start the OrcleDBConsole.

6. Open  emoms.properties again and Search for:

a)oracle.sysman.eml.mntr.emdRepPwd=

verify  that the password is encrypted

b) oracle.sysman.eml.mntr.emdRepPwdEncrypted=

verify  that the value is set to  TRUE

7. Refresh Oracle Enterprise Manager